Mechanical vacuum pump



3,iso,559

J. R. BOYD MECHANICAL VACUUM PUMP April 27, 1965 6 Sheets-Sheet 1 FiledApril 11, 1962 INVENTOR.

JOHN R. BOYD A TTORNE Y5 J. R. BOYD A ril 27, 1965 6 Sheets-Sheet 2Filed April 11, 1962 INVENTOR. JOHN R. BOYD My A Tram/5Y3 April 27, 1965J. R. BOYD MECHANICAL VACUUM PUMP 6 Sheets-Sheet 3 Filed April 11, 1962Fl a. 6

FIG. 8

6 Sheets-Sheet 4 Filed April 11, 1962 IiVVENTOR. JOHN R. BOYD BY5%[062'9 A TTOR/VE Y5 April 1965 J. R. BOYD 3,180,559

MECHANICAL VACUUM PUMP Filed April 11, 1962 6 Sheets-Sheet 5 '62INVENTOR.

JOHN R. BOYD Fm. l6 BY wmzfiw d/ Aprii 27, 1965 J. R. BOYD 3,180,559

MECHANICAL VACUUM PUMP Filed April 11, 1962 6 Sheets-Sheet 6 *F u. 20 2x u. w O '5 1o 2 3 0 IO 3O w 10 w FLOW RATE Ibs/minufe Fae. l8

now RAIE- CcFm) 5 10 w I 500 I000 PRESSURE (mm Hg) Fm. l9

INVENTOR. JOHN R. BOYD BY m VMMW A TTO/E'NEVS United States PatentOfiice 3,l80,55 Federated Apr. 2?, 1955 3,186,559 MECEANECAL VACUUM PUMPJohn R. Boyd, 23011 Capistrano Way, Los Altos, Calif. Filed Apr. 11,1962, Ser. No. 187,461 39 Claims. (Cl. 236142) The present inventiongenerally relates to mechanical Vacuum pumps and more particularlyconcerns an improved vacuum pump comprising two intermeshing andsynchronized rotors.

Although the invention will be described from the standpoint of itsembodiment as a vacuum pump device, it will be appreciated that certainfeatures of the apparatus are equally applicable to equivalentmechanical devices.

Vacuum pump technology has been directed towards the objective ofachieving a maximum vacuum condition in a minimum amount of time and atminimum expense.

A major problem in this regard has been the necessity of creating a sealto adequately enable the creation of a maximum vacuum condition, andtowards this end the prior art has shown a substantial reliance upon oilseals of one type or another. Thus, oil-diffusion pumps and oilsealedmechanical pumps are conventional in many types of vacuum systems. Itwill be appreciated, however, that oil molecules even in very smallconcentration create very serious problems in most types of vacuumprocesses. Modern vacuum technology in certain areas requires a veryclean vacuum, particularly for operations such as vacuum tubeprocessing, precision thin film deposition, particle ac celeratorevacuation and the like.

Vacuum pump design within the limitations to which the present inventionis directed has usually been based upon the ejector principle, thepiston-cylinder principle, or the eccentric rotary vane principle. Morerecently, the molecular pump has been employed. Each of these devicesappears to be characterized by one or more problems related to oilcontamination of the vacuum system, low flow rates, pulsationcharacteristics, shortened life, or expensive production.

More basically, these devices employ a design structure which inherentlyresults in a relatively slow vac-uum formation (excepting the ejectorunit which is not appropriate for maximum vacuum conditions unless anexotic working medium such as mercury is used) whereby undesirable fiuidleakage and heat transfer may occur.

One object, therefore, of the present invention is to provide animproved vacuum pump which is inherently designed to have a minimumdegree of fluid leakage and heat transfer, particularly at the point inits cycle wherein it approaches the maximum vacuum condition.

Another object of the present invention is to provide an improved vacuumpump requiring no oil seals or other fluid seals of any type.

Another object of the present invention is to provide an improved vacuumpump which enables a relatively high flow rate and yet a minimum totalweight for the unit, which requires no valves, and which acts to createits own molecular seal because of supersonic flow conditions attained.

Still another object of the present invention is to provide an improvedvacuum pump which is particularly designed for operation in the vacuumspectrum between or lower Torr and atmospheric pressure, and which maybe produced at a relatively low manufacturing cost to have relativelylong life with minimum maintenance.

Still a further object of the present invention is to provide animproved vacuum pump which is characterized by compression ratios ten totwenty times greater than equivalent conventional units, and yet whichmay be constructed in a compact design to comply with the aforegoingobjects.

These and other objects of the present invention are generally achievedby providing an improved fluid vacuum pump comprising a casing having aninlet thereto and an outlet therefrom for drawing in and ejecting themedium being pumped, respectively.

A piston rotor and a cylinder rotor are mounted for rotation within thecasing, and the rotors are designed to have intermeshing lobes andgrooves co-functioning with each other and with the casing to effectejection of the fluid.

The terms piston and cylinder are used throughout the specification andclaims in describing the lobed rotor and grooved rotors, respectively,since these terms indicate functionally the action of these respectiverotors.

As an important feature of the invention, each of the lobes and thegrooves is characterized, respectively, by a radially extending matingflat surface designed to effect maximum displacement of fluid with aminimum rotational movement of the rotors.

In addition, some type of driving means for eifecting rotation of therotors is provided.

A better understanding of the present invention will be had by referenceto the drawings, disclosing merely one illustrative embodiment, and inwhich:

FIGURE 1 is a perspective view of the improved vacuum pump, according tothe present invention, disclosing in part an inlet and outlet therefromfor passage of fluid therethrough and also disclosing schematically theconnection to a source of power;

FIGURE 2 is a cross section through the vacuum pump of FIGURE 1 taken inthe direction of the arrows 22;

FIGURE 3 is a cross-sectional View taken in the direction of the arrows3-3 of FIGURE 2 disclosing the inter meshing of the rotors and thedisposition of same within the casing;

FIGURE 4 is a perspective view of the piston rotor shown in FIGURES 2and 3 on a somewhat difierent scale;

FIGURE 5 is a view taken in the direction of the arrows 55 of FIGURE 4indicating the spiral of the lobes of the piston rotor;

FIGURE 6 is a side elevation of the piston rotor shown in FIGURES 2, 3,and 4 also disclosing the helical nature of the lobes formed thereon;

FIGURE 7 is a view taken in the direction of the arrows 7-7 of thepiston rotor of FIGURE 6 disclosing certain geometrical relationshipsembodied in the piston rotor, including the left-hand helical spiral;

FIGURE 8 is an enlarged detailed view in cross section of one of thelobes of the piston rotor of FIGURE 5;

FIGURE 9 is a side elevation of the cylinder rotor shown in FIGURES 2and 3 disclosing the right or left hand helical-spiral form of thecylindrical grooves embodied therein;

FIGURE 10 is a view of the rotor of FIGURE 9 taken in the direction ofthe arrows til-Ill disclosing in more detail the geometricalrelationships of the grooves formed therein;

FIGURE 11 is an enlarged cross-sectional view of one of the grooves ofthe cylinder rotor shown in FIG- URE 10;

FIGURE 12 is an enlarged cross-section of an intermeshing lobe andgroove of the piston and cylinder rotors illustrating velocity vectorrelationships;

FIGURE 13 is a time versus volume chart indicating degree of volumechange per unit time rate;

FIGURE 14 is a schematic representation of the vacuum pump of thepresent design illustrating a preferred manner of drawing fluid into theunit;

FIGURE 15 is a schematic representation of the vacuum'pump of thepresent invention embodied in a two- 'stage arrangement;

' .FIGURE 16 schematically indicates two pumps in ent invention,embodying a tapered casing 10 of gener ally rectangular cross section(see FIGURE 3). The casing 10 has connected thereto and communicatingwith the'interior thereofan inlet 12 and an outlet 14. The inlet 12 isshown in FIGURE 1 in an alternative position for illustrative purposes,the preferred construction being shown in FIGURE 14 to be describedhereafter. The in- -let 12 is designed to receive fluid from the spaceor chamber being evacuated, said fluid being drawn into the easing 10,.and then expelled or ejected through the outlet 14 after pumping actionhas occurred.

Preferably, the casing 10 has coupled thereto at its right hand end (asviewed in FIGURE 1) an end bracket 16 which in' turn is partiallyenclosed by a gear housing 18 through which extends an input shaft 20.The shaft 20 is designed to be coupled to any type of suitable drivingmechanism or source of power as schematically indicated, although anelectrical motor is preferred.

The internal construction of the vacuum pump may be more clearlyunderstood by reference to FIGURE 2. The shaft 20 is journalled in abearing 22 in the gear housing 18 and connects in a conventional mannerwith bevel gears 24 and 26. 'The bevel gears are in the ratio of 2 to 3with the driving gear or gear 26 having in one embodiment thirty-eightteeth and the driven gear fiftyseven teeth. Y

The gear housing may be connected with bolts or screws 28 into tappedholes in the end bracket 16. Similarly, the end bracket 16 as. such maybe connected with Allen screws or the like 30 into tapped'holes in themain casing 10.

Disposed within the end bracket 16 is a duplex bearing 32 journalling ashaft 34 which may be integral with shaft 20 or which may be coupled insome manner thereto. The shaft 34- passes through the axial center ofand is designed to drive the piston rotor 36. Similarly, a duplex 7bearing 38 is also provided Within the end bracket 16 within which ashaft 40 is journalled, the latter being de-' signed to drive a cylinderrotor 42. The gear 24 is, of course, coupled to the shaft40 as is thegear 26 coupled 'to theshaft 34 such that the input shaft 24 will effectrotation of the rotors 36 and 42 in opposite directions.

k In one form,the shaft 40 may be keyed at 44 to the cylinder rotor 42,while the shaft 34 is keyed at '46 to the pistonrotor 36, as clearlyshown in the view of 7 FIGURE 3;

'trative unit is concerned.

16 and the cylinder rotor 42. These discs are preferably of asemi-metallic composition so as to have the characteristics of long wearand low friction, thereby suitably sealing off the end faces of therotors 36 and 42 while at the same time not creating any substantialfrictional force upon the rotors 36 and 42. Similar disc-like seals ofthe same composition may be provided at the opposite ends of the rotors36 and 42 as indicated by the numerals 52 and 54.

It will be evident from the view of FIGURE 2 that the rotors 36 and 42have their axes disposed at an angle one to the other such that they arenot in parallel alignment. Thus, in the embodiment shown and described,the angle approximates 1436 although variations of plus or minus sevendegrees are believed feasible. From the standpoint of manufacturing andprecision construction, it is desirable that some means be employed topositively index the rotors in position within the casing 10. Inserts 56and 58 are provided for this purpose. Inserts 56 and 58 are designed tohave their inner sides positioned adjacent the seals 52 and 54 withtheir outer sides being against the end bracket 60 on the left hand endof the unit as viewed in FIGURE 2. The inner faces of inserts 56 and 58are canted with respect to their outer faces at precisely the same angleas the axes of the rotors 36 and 42 diverge from each other. such thatprecise positioning of these rotors may be effected to obtain optimumvacuum conditions as will be hereafter described.

The end bracket 60, as such, may be fastened with screws or bolts 62 tothe casing 10.

Disposed within the end bracket 60 is a'bearing 64 having'an enclosingbearing cap 66 provided with fastening disc 50 is axially interposedbetween the end bracket to be received within bearing 64.

Similarly, the left hand end of shaft 40 is received within bearing 70which is enclosed with a bearing cap 72 secured with screws or bolts 74.Conventional bearings suitable for the particular design of the unit maybe employed. I

It will be noted from the view of FIGURE 1 that two sides of the casing10, sides 10a and 1012 are parallel to the axes of the rotors 36 and 42.On the other hand, as clearly shown in FIGURE 2, the other sidewalls ofthe casing 10 are designed to be tapered in accordance with the angledefined between the axes of the rotors 36 and 42 which in turn followsfrom the taper characterizing the rotors as such. Thus, the sidewalls10a and 10b are tapered in a direction parallel to the axes of theenclosed rotors, respectively. As a consequence of this construc tion,gauging and precision construction during manufac ture can besimplified. In this regard, it is of interest to note that the precisiongaugingof the pump requires free running clearances of approximately0.003 inch.

A more detailed explanation of the construction of the piston andcylinder rotors36 and 42, respectively, may now be had by reference toFIGURES 3-10.

' In the cross section taken in FIGURE 3, it Will be seen that thepiston rotor 36 is provided with eight lobes or semi-pistons while thecylinder rotor 42 is provided with v a twelve grooves designed to matewith the lobes of the 78, i.e., 8:12. In consequence, the diameter onthe pitch line of the piston rotor 36 is in the ratio of two to threewith the diameter on the pitch line of the cylinder rotor 42. Althoughother ratios may be employed, it has been found that this particularratio is advantageous for maximum vacuum efficiency insofar As will beevident-from the view of FIGURE'4, the piston rotor 36 is provided withlobes '76, as heretofore as the design of the illusidentified, whichtwist to the left in the form of a spiralhelix or screw (see also FIGURE5) to complete one turn of 360 degrees from the larger diameter end ofthe rotor to the smaller diameter end, as indicated by lobe line L andpoints P and P In the view of FIGURE 4, the shaft is not shown in theunit, whereby the internal axial bore 80 is indicated. The cylinderrotor is similarly provided with a bore 82, as shown in FIGURE 9. Thecylinder rotor 42 (not shown in perspective) is also provided withgrooves '78 which complete approximately one 240 degree twist (in thesame ratio of 2:3 heretofore discussed) throughout the length of therotor; however, in the case of the cylinder rotor, the twist is to theright or in a clockwise direction as viewed from the large end of therotor. These twists are better shown and described in conjunction withFIGURES 6 and 9.

As shown in FIGURE 6 and heretofore mentioned, the piston rotor 36 isprovided with lobes forming a lefthanded 360 degree twist as indicatedschematically by the line 84. In actual construction, it is alsodesirable to form the larger end 85 of the rotor with beveled lobe edges86, the bevel being at an angle of 1436 with respect to a plane normalto the axis of the rotor 36. This bevel is provided for manufacturingpurposes and to obtain maximum vacuum conditions.

Similarly, the small end 87 of the rotor is provided with an angled orbeveled indentation or recess 88 for the same purpose. It will be notedthat the depth of the groove or lobe is measured from the pitch circleor point at which the angled edge merges into the rectilinear endsurface (85 or 87) to the outer periphery of the unit as indicated bythe numeral 90. Thus, the beveled edge 86 at the smaller end and thebeveled edge 88 at the larger end are merely indicative of the ends ofthe lobes 76.

These beveled lobe ends 86 and $8 assist in approximating a sphericalsurface to in turn maximize the vacuum action of the unit.

Although precise dimensions do not appear to be critical, dimensionshave been indicated in FIGURES 6-11 of one experimental model built. Inthis regard, it should be noted (as heretofore mentioned) that thepreferred angle between the axes of the piston and cylinder rotors is1436 or the same angle as the bevel 86 and 88. The angle between theaxis of the cylinder rotor 42 and the center line of the unit issomewhat greater than the angle between the axis of the piston rotor 36and the same center line.

It is to be noted that the angle n 5 or that the lobes become more andmore parallel to the axis towards the smaller end of the piston rotor7e. As a consequence of this construction, once a given force is exertedon the particular fluid medium, the resistance to movement thereof isgradua ly decreased so that added acceleration is given to the fluid asit reaches the outlet 14. In the illustrative embodiment, the differencebetween u and 5,, is approximately 40 although the angle is not believedcritical.

Referring now to the view of FIGURE 7, it will be seen that the pitchcircle is defined by the inner points of the lobes 76, as indicated at92. In order to form the lobes 76, the outer circular periphery 94 ofthe rotor 36 is di vided into 45 degree sections or lines 96. Thus,looking at the view of FIGURE 8, the line 95 at its point ofintersection with the pitch circle 92 defines a point forming a radiusto form that part of the lobe extending from the points a to b. Thisradius in the particular construction illustrated is .635 inch.Thereafter, a radius is used of .234 inch, said radius being measuredalong the 45 degree line 36 radially inwardly and being employed to formthe portion bc of the lobe 76X. Thereafter, between the points 0-4:, astraight line is used. This straight line or rectilinear portion 76Xforms the flat portion of the lobe which functions very importantly inthe ultimate degree of vacuum produced for the work expended. The pointd is found by a radius of 1.730 inches (see FiG- URE 7) from the axis ofthe unit being drawn to connect with the surface formed by the .234radius between points 15 and c. In one form of the invention, the flator rectilinear portion c-d would continue to e, the latter connectingwith f on the pitch circle 92. In a preferred form of the invention,however, the pitch circle portion extends between 24 or .025 inchfurther such that the portion d-e is slightly angled with respect to theportion cd.

It will thus be seen that the lobe 76X is formed predominantly of aradiused portion a-b and a flat portion c-d with connecting portionsb-c, d-e, and 6-1. It is believed from experiments that the flat portionc(l is the portion of the lobe that lends the greatest novelty to thepresent invention insofar as the intermeshing construction of the rotorlobes and grooves are concerned. Test runs indicate that as this flatportion mates with the congruous fiat portion of the cylinder rotorgroove that the maximum compression of the medium occurs.

The construction of the cylinder rotor 42 and the grooves thereof maynow be described by reference to FIGURES 9-11. It will be found thatmost of the elements are analogous for cofunctioning operation.

Thus, looking at the view of FIGURE 9, it will be seen that the cylinderrotor 42 is provided with an approximate 240 degree twist to itsgrooves, as indicated schematically by the numeral 98. In this instance,as previously stated, the twist 98 extends radially towards the right orclockwise as viewed from the larger end of the cylinder rotor 42. Also,the cylinder rotor is provided with a beveled edge 1th at its larger endand a recessed beveled edge 102 at its smaller end, these edges formingthe marginal edges of the grooves 78 and functioning similarly to lobeends 86 and 88. Thus, the groove depth may be indicated by the numeral104. It will also be noted that oc ,8 analogously to u being less than5,, as heretofore mentioned in connection with the piston rotor.

Referring to the view of FIGURE 10, it will be seen that the cylinderrotor 42 is formed in a somewhat similar manner as the piston rotor 36.In this instance, the pitch circle is indicated at 108, while the 30degree lines are indicated at 110. The same radii are employed betweensimilarly designated'points. Thus, as seen in FIGURE 10, the portion a-bis formed by a radius taken from the 30 degree line of .635 inch.Thereafter, a radius of .234 inch from the point b along the same line11% of 30 degree line is used to form the surface bc and identicalmeasurements as heretofore described in conjunction with FIG- URE 8 areused to form the portion c-d, d-e, e',f and 6-)".

Thus, the groove 78X which is exemplary of all the grooves 78 of thecylinder rotor 42 is also formed with a flat portion cd functioning tocreate the high vacuum area with its mating fiat portion c-d of the lobe76X. Again, the groove 78X is formed with a large radiused portion a-bwhich mates with the portion (1-12 of the lobe 76X. Other connectingportions are similar.

It has been found with this type of construction that the mating lobesand grooves tend to create a superharmonic motion or cycle in theejection and drawing induction of the fluid medium. It is believed thatthis action occurs as a consequence of the face-to-face relationship ofthe fiat portion cd of the lobes 76 and grooves 78 whereby a very highnearly complete fast vacuum condition is effected along a center line ofthe apparatus as contrasting the four link slider action of apiston-cylinder, for example, which creates a vacuum very slowly.Furthermore, it is also of interest to note that this flat-to-flatarrangement simplifies the manufacture by enabling more simple gaugingof the spiral angle of twist.

As a consequence of the 2:3 ratio characterizing the diameters, numberof lobes versus grooves, and degree of twist of the piston-cylinderrotor combination, an advantageous geometrical relationship occurs whichtends to assist in the displacement of fluid media and the accompanyingvacuum action.

Thus, in FIGURE 12, there is shown one of the lobes drawn to intersectthe line from A 76 of piston rotor 36 intermeshing with a groove 78 ofcylinder rotor 42. The axis of the cylinder rotor 42 is indicated bypoint A and the axis of the piston rotor 36 by point A If lines aredrawn from points A and A to theend of a vector V (indicating thekinetic velocity common to both rotors 36 and 42 on the engaging pitchline thereof), a relative indication of the velocity of tip of lobe 76,as shown by V may be had as against theivelocity of the inner surface ofthe groove 78, as shown by V Thus, V represents the vector drawn tointersect the line from A while V represents the vector The ditferenceor V V represents the shear velocity V or a'molecular drag actiontending to increase the vacuum characteristics of the unit.

Although applicant does not desire to be bound by the theory explainedherein and set forth in the illustrative charts, reference may be madeto FIGURE 13 for a further explanation of the type of super-harmonicmotion created by applicants novel rotor device. In this view, thenumeral 120 designates a curve indicating applicants approximatevariation in volume measured againsttime. In this curve, the portion a-bmay represent the intermeshing radiused portion and the portion c-d mayrepresent the flat-to-flat intermeshing. It will be seen that theflatportion c-d rises much more closer to the vertical than does theequivalentportion of the curves 122 and 124. Curve 2 designated bynumeral 124 may indicate partial superharmonic motion, while the curve ydesignated by numeral 122 may indicatesimple harmonic motion such aswould characterize a piston-cylinder arrangement of a vacuum pump. Thus,with applicants improved vacuum pump, a very quick increase in volumeoccurs (see FIGURE 13) during the flat-to-flat intermeshing of portionc-d with a gradual breaking away during the radiused mating portions a-bof grooves 76 and lobes 78 of the respective rotors.

Of course, the general principle of screw types of rotors forcompression is well known in the art, and applicant makes no claim tosame as such.

In the use of the improved vacuum pump, it is, desirable that the inlet12, as indicated in FIGURE 1, preferably be formed as a Y-shaped inlet126, as indicated in FIGURE 14. Preferably, the two legs 126a and 126bof the Y-shaped inlet should be formed so as to be aligned with or openinto the interior of the casing with a particular lobe and grooveintermeshing with each other approximately one-sixth to one-half thelength of the rotors measured from the inlet end of the rotors or thelarge ends thereof. A preferred point is approximately one-third thelength.

The main factor in this regard is to have the inlet open into the centerline of the apparatus at a point at which a substantially maximum vacuumis attained. Thus, it is not desirable to have the inlet open directlyinto the end of the unit since maximum vacuums are not attained in thatportion of the pump. Furthermore, it is not preferred to 8 which may beprovided with bearings 154 and 156 as indicated. .A center casing 158may serve to enclose the high speed coupling 150 and maintain the vacuumconditions therein.

. It will be appreciated that a similar construction only furtherextended may be employed for further stages if desired. Thus, FIGURE 16illustrates diagrammatically two pumps 160 and 162 connected-in parallelto a third pump 164 in series. Designations V and Y merely indicate twoseparate sources of media or fluids. FIGURE 17 illustrates schematicallythree stages in series, as by pumps 170, 172, and 174. Constructiondetails may be similar to those disclosed in FIGURE 15.

FIGURES 18 and 19 are merely included to give further indication of thecharacteristics of one experimental model of the improved vacuum pumpconstructed in accordance with the present invention. It is, of course,expected that improved results will be obtained as further refinementsare made. 7

It is believed that the operation of the improved vacuum pump, accordingto the present invention, has been clearly described in connection withthe foregoing specification. Instrumentation indicates that the fiowvelocity is such that supersonic speeds are attained whereby the fluidor gas tends to create its own seal with the interior of the casing. Inconsequence, the oil seals associated with conventional apparatus areeliminated although the unit is still capable of achieving high vacuumconditions. Pressure ratios have already been measured in theexperimental prototype built of one to twenty thousand at the inlet 12.

At the present time, it cannot be precisely stated the extent to whichthe various dimensions may be varied, particularly with respect to theshape of the lobes 76 and the grooves 78. However, it can be stated thatit is preferred to have the diameter of the cylinder rotor greater thanthe diameter of the piston rotor and the cylinder rotor to have agreater number of grooves than the piston rotor has lobes. In addition,it is believed essential to the present invention that the mating lobes76 and grooves 78 have a flat-to-flat intermeshing portion.

Although the precise location of the fluid inlet may be varied asheretofore described, its position at approximately one-third the lengthof the unit measured from the larger end thereof'is desirable. Theprecise positioning of the outlet may be varied. Also, as mentioned, the

. included angle between the axes of the grooved rotor and lobed rotormay possibly be varied to a certain extent, but it is preferred that itbe within plus or minus 7 degrees of the angle shown.

The pump as illustratively described has-as heretofore indicatedbeenconstructed and operated. The

V rotors have been turned as fast as 25,000 rpm. with satis have theinlet come into the upper part of the unit, as

shown in FIGURE 1, since the possibility of back pressure exists asdetermined experimentally although such inlet could connect with thesame rotor-groove combination.

The schematic illustration of FIGURE 15 has merely beenprovided toindicate that the vacuum pump of the present invention may be readilyproduced to be employed in multistage applications. Thus, lookingat theview of FIGURE 15, there is schematically indicated a motor 140 factoryresults. It will be noted that the tapered rotors in combination withthe duplex bearings yield a configuration characterized by arelativelylow torsional resonant frequency. In this regard, it will be appreciatedthat the center of gravity of each rotor is considerably closer to thelarger end. 7

It will be appreciated that other portions of the improved vacuum unit,such as the driving means, the gearings, the bearings, the inserts, theseals, and other components which may be associated with the finalassembly may be :varied in consruction and dimensions. The di mensionsshown herein are therefore not to be thought of as limiting, but merelyillustrative for the purpose of giving a complete teaching of theinvention in one of its embodiments.

- It will be evident to' those skilled in the art that variousmodifications and changes may be'made in certain portions of theimproved vacuum unit without departing from the spirit and scope of theinvention ther'eofrsuch scope of the following claims.

What is claimed is:

1. An improved fluid vacuum pump comprising:

(a) acasing;

(b) an inlet to said casing for said fluid;

(c) an outlet from said casing for said fluid;

(a') a piston rotor and a cylinder rotor mounted for rotation withinsaid casing;

(e) said piston and cylinder rotors having intermeshing spirming lobesand grooves, respectively cofunctioning with each other and with saidcasing to effect induction and ejection of said fluid;

(f) each of said lobes and said grooves being characterized,respectively, by a radially extending mating rectinlear flat surfacedesigned to effect maximum displacement of fluid with a minimum movementof said rotors; and,

(g) means for synchronized driving of said rotors.

2. An improved fluid vacuum pump, according to claim 1, in which saidlobes and grooves, respectively, define a helix on the periphery of saidpiston rotor and cylinder rotor.

3. An improved fluid vacuum pump, according to claim 1, in which saidrotors are each tapered in the same direction and are of frusto-conicalshape such that the axes thereof are non-parallel and converge to definean angle therebetween.

4. An improved fluid vacuum pump, according to cla ms 3, in which theoverall diameter of each of said rotors decreases in a direction fromsaid inlet to said outlet.

5. An improved fluid vacuum pump, according to claim 1, in which:

(a) said lobes and grooves, respectively, define a helix on theperiphery of said piston rotor and cylinder rotor; and,

(b) in which said rotors are each tapered in the same direction and areof frusto-conical shape such that the axes thereof are non-parallel todefine an angle therebetween.

6. An improved fluid vacuum pump, comprising:

(a) a casing;

(b) an inlet to said casing for said fluid;

(c) an outlet from said casing for said fluid;

(d) a piston rotor and a cylinder rotor mounted for rotation within saidcasing, said rotors being designed to, respectively, have intermeshinglobes and grooves co-functioning with each other and with said casing toeffect induction and ejection of said fluid, said piston rotor beingcharacterized by a smaller overall diameter than said cylinder rotor atany given axial position, and defining fewer lobes than said cylinderrotor defines mating grooves;

(e) each of said lobes and said grooves being characterized,respectively, by a radially extending mating rectilinear flat surfacedesigned to effect maximum displacement of fluid With a minimum rotationof said rotors; and,

(f) means for synchronized driving of said rotors.

7. An improved fluid vacuum pump, according to claim 6, in which saidrotors are each tapered in the same direction and are of frusto-conicalshape such that the axes thereof are non-parallel and converge to definean angle therebetween.

8. An improved fluid vacuum pump comprising:

(a) a casing;

(b) an inlet to said casing for said fluid;

(c) an outlet from said casing for said fluid;

(d) a piston rotor and a cylinder rotor mounted for synchronizedrotation Within said casing, said rotors being designed to, espectivery,have inter-meshing helically formed lobes and grooves co-functioningwith each other and with said casing to effect induction and ejection ofsaid fluid, each of said lobes and said grooves being characterized,respectively, by a radially extending mating rectilinear flat surface iddesigned to effect maximum displacement of fluid with a minimum movementof said rotors; and,

(e) each of said rotors being tapered in the same direction so as to beof frusto-conical shape whereby the axes thereof are non-parallel andconverge to define an angle therebetween; and,

(f) means for driving said rotors.

9. An improved fluid vacuum pump, according to claim 8, in which saidlobes characterizing said piston rotor effect approximately a 360 degreetwist from the large end of said piston rotor to the small end of saidpiston rotor; and, in which said grooves characterizing said cylinderrotor effect approximately a 240 degree twist from the large end of saidcylinder rotor to the small end thereof.

10. An improved fluid vacuum pump, according to claim 8, in which saidinlet is located so as to communicare with a center line lobe-groovecombination approximately one-sixth to one-half the axial length of saidrotors measured from the large ends thereof.

11. An improved fluid vacuum pump comprising:

(a) a casing;

(32) an inlet to said casing for said fluid;

(c) an outlet from said casing for said fluid;

(r!) a piston rotor and a cylinder rotor mounted for synchronized,intermeshing rotation within said casing;

(c) said rotors being designed to have helically formed lobes andgrooves co-functioning with each other and with said casing to effectinduction and ejection of said fluid;

(l) each of said lobes and said grooves being characterized respectivelyby a radially extending mating rectilinear flat surface designed toeffect maximum displacement of said fluid with a minimum move ment ofsaid rotors;

(g) each of said lobes on said piston rotor defining an approximate 360degree twist in one direction from the large end thereof to the smallend thereof, and each of said grooves on said cylinder rotor defining anapproximate 240 degree twist in an opposite direction from the large endthereof to the small end thereof;

(it) said piston rotor and said cylinder rotor being tapered in the samedirection and each being of frusto-conical shape such that the axesthereof are nonarallel and converge to define an angle therebetween;and,

(1') means for driving said rotors to eifect induction of fluid to saidinlet and ejection of fluid through said outlet.

12. An improved fluid vacuum pump, according to claim 11, in which theinlet to said casing is located so as to communicate with a lobe-groovecombination axially disposed approximately one-sixth to one-half theaxial length of said rotors from the large ends thereof.

l3. An improved fluid vacuum pump, according to claim 12, in which saidinlet is located so as to communicate with a lobe-groove combinationone-third the axial length of said rotors measured from the large endsthereof.

14. An improved fluid vacuum pump, according to claim 11, in which saidpiston rotor at any given axial position thereof has a lessercross-sectional area than said cylinder rotor at a corresponding crosssection thereof.

15. An improved fluid vacuum pump, according to claim 11, in which saidpiston rotor has an overall diameter two-thirds the diameter of saidcylinder rotor at any given axial point and in which said piston rotorhas two-thirds as many lobes as said cylinder rotor has grooves.

16. An improved fluid vacuum pump comprising:

(a) a casing;

(b) an inlet to said casing for said fluid;

(c) an outlet from said casing for'said fluid;

(d) a piston rotor and a cylinder rotor mounted for rotation with saidcasing;

- (e) said rotors being designed to have intemieshing lobes and groovesco-functioning with each other and with said casing to effect inductionand ejection of said fluid;

(f) each of said lobes and said grooves being characterized,respectively, by a radially extending mating rectilinear flat surfacedesigned to effect maximum displacement of fluid with a minimum movementof said rotors;

(g) each of said lobes and said grooves defining a helix on the surfaceof said rotors, respectively, the angle of said helix changing from oneend of each 'of said rotors to the other end thereof; and,

(It) means for driving said rotors in synchronization.

17. An improved fluid vacuum pump comprising:

(a) a casing;

(b) an inlet to said casing for said fluid;

(c) an outlet from said casing for said fluid;

(d) a piston rotor and a cylinder rotor mounted for rotation within saidcasing;

(e) sa id rotors being designed to have intermeshing lobes'and groovesco-functioning with each other and with said casing to effect inductionand ejection of said fluid;

(f) each of said lobes of 'said piston rotor and each of said grooves ofsaid cylinder rotor being characterized, respectively, by a radiallyextending mating rectilinear flat surface designed to effect maximumdisplacement of fluid with a minimum movement of said rotors;

(g) 'said piston rotor and said cylinder rotor being tapered in the samedirection and being of frustoconical shape such that the axes thereofare nonparallel and converge to define an angle therebetween;

(h) each of said lobes of said piston rotor and each of said grooves ofsaid cylinder rotor defining a helix about the body of the respectiverotors, said helix being in the form of an angularly decreasing twistfrom the large end to the small end of said rotors, respectively; and,

(i) means for driving said rotors so as to effect induction'of saidfluid through said inlet and out through said outlet of said vacuumpump.

18. An improved fluid vacuum pump, according to claim 17, in which saidtwist characterizing said piston rotor approximates 360 degrees from thelarge end of said piston rotor to the small end thereof, and in whichthe twist characterizing said cylinder rotor approximates 240degreesfrom the large end of said cylinder rotor to the small end thereof.

19. An improved fluid vacuum pump, according to claim 17, in which theinlet of said casing is located so as to communicate with a matinglobe-groove combination intermeshing at a point one-half to one-sixththe axial length of said rotors measured from the large ends thereof. V

20. An improved fluid vacuum pump, according to claim 17, in which saidpiston rotor has fewer lobes than said cylinder rotor has grooves, andin which said piston rotor has a smaller overall diameter than saidcylinder rotor has 'at any given axial point on the center line'of (c)said rotors each being tapered in the same direction and being offrusto-conical shape such that the axes thereof are non-parallel andconverge to define an angle therebetween;

I rotor and the helix characterizing said cylinder rotor de- 7 (f) saidcasing having a pair of opposing sidewalls parallel to the respectiveaxes of said piston rotor and said cylinder rotors;

(g) said rotors being designed to have intermeshing spiralling'lobes andgrooves co-functi-oning with each other and with said casing to effectinduction and ejection of said fluid;

(h). each of said lobes and said grooves being characterized,respectively, by a radially extending mating rectilinear flat surfacedesigned to effect maximum displacement of fluid with a minimum movementof said rotors; and,

(1') means for driving said rotors in synchronization so as toetfectinduction of said fluid through said inlet and ejection of said fluidthrough said outlet of said pump.

22. An improved fluid vacuum pump, according to claim 21, in which saidlobes and grooves, respectively, define a helix on the periphery of saidpiston rotor and said cylinder rotor, respectively.

23. An improved fluid vacuum pump, according to claim 21, in which theoverall diameter of said cylinder rotor and said piston rotor decreasesin a direction from said inlet to said outlet;

24. An improved fluid vacuum pump, according to claim 21, in which theangle of twist characterizing said spiralling lobes and grooves,respectively on said piston rotor and said cylinder rotor decreases in adirection from the large end to the small end of said rotor, such thatsaid helix more closely approaches being parallel to the axes of saidrotors, respectively.

25. An improved fluid vacuum pump, according to claim 21, in which saidangle of twist of said piston rotor is approximately 360 degrees fromthe large end tothe small end thereof in one direction and in which theangle of twist for said cylinder rotor is approximately 240 degrees fromthe large end to the small end thereof in an opposite direction.

. 26. An improved fluid vacuum pump comprising:

(a) a casing; d

(b) an inlet to said casing for said fluid;

(c) an outlet from said casing for said fluid;

(d) a piston rotor and a cylinder rotor mounted for rotation Within saidcasing;

(e) said' rotors being designed to have intermeshing spiralling lobesand grooves co-functioning with each other and with said casing toeffect induction and ejection of said fluid;

(1) each of said lobes and said groves being characterized,respectively, by a radially extending mating rectilinear flat surfacedesigned to effect maximum displacement of fluid with a minimum movementof said rotors, and a radiused mating portion embracing approximatelyraquarter circle; and,

(g) means for driving said rotors insynchronization.

27. An improved fluid vacuum pump, according to claim 26, in which saidrotors are each tapered in the same direction and are of frusto-conicalshape such that the axes thereof are non-parallel and'converge to definean angle therebet-Ween.

28. An improved fluid vacuum pump, according to claim 26, in which saidcasing defines opposing sidewalls ,parallel, respectively, to therespective axes of said rotors.

2-9. An improved fluid vacuum pump, according to claim 26, in which thelobes of said piston rotor define a helix on theperiphery thereof andthe grooves of said cylinder rotor define a helix on the peripherythereof.

30. An improved fluid vacuum pump, according to claim 29, in whichthe'helix characterizing said piston creases 'in its angle relative tothe axes of said respective rotors fromthe largeend to the small endthereof.

7 (References on following page),

References Cited by the Examiner UNITED STATES PATENTS 3/84 Troutrnan103-126 9/31 Monteiius 103128 6/ 49 Whitfield 103-128 7/49 Paget 23014312/52 Niisson 230--143 10/59 Rich et a1. 103-128 1/63 Borden 103128FOREIGN PATENTS 5/55 France.

10 KARL J. ALBRECHT, Primary Examiner.

Germany.

Great Britain. Great Britain. Great Britain. Great Britain. GreatBritain. Great Britain.

Switzerland.

WILBUR I. GOODLIN, JOSEPH H. BRANSON, 1a.,

Examiners.

1. AN IMPROVED FLUID VACUUM PUMP COMPRISING: (A) A CASING; (B) AN INLETTO SAID CASING FOR SAID FLUID; (C) AN OUTLET FROM SAID CASING FOR SAIDFLUID; (D) A PISTON ROTOR AND A CYLINDER ROTOR MOUNTED FOR ROTATIONWITHIN SAID CASING; (E) SAID PISTON AND CYLINDER ROTORS HAVINGINTERMESHING SPIRALING LOBES AND GROOVES, RESPECTIVELY COFUNCTIONINGWITH EACH OTHER AND WITH SAID CASING TO EFFECT INDUCTION AND EJECTION OFSAID FLUID; (F) EACH OF SAID LOBES AND SAID GROOVES BEING CHARACTERIZED,RESPECTIVELY, BY A RADIALLY EXTENDING MATING RECTINLEAR FLAT SURFACEDESIGNED TO EFFECT MAXIMUM DISPLACEMENT OF FLUID WITH A MINIMUM MOVEMENTOF SAID ROTORS; AND, (G) MEANS FOR SYNCHRONIZED DRIVING OF SAID ROTORS.